Wheelchair automatic anti-rollback assembly

ABSTRACT

An anti-rollback assembly adapted or adaptable for use in combination with a wheelchair. The anti-rollback assembly includes a one-way brake assembly automatically immobilizing the wheelchair against rearward movement when the occupant attempts to rise from or sit in a seat member of the wheelchair, yet at the same time does not prevent the wheelchair from moving in a forward direction. Conversely, when the occupant is fully seated in the seal member, the one-way brake assembly is disengaged so that the wheelchair can move freely in forward or rearward directions. The assembly can be retrofitted onto existing wheelchairs, and is adjustable to fit various size wheelchairs.

This is a continuation of application Ser. No. 09/026,902, filed Feb.20, 1998, now U.S. Pat. No. 6,092,824. This application claims thebenefit of Provisional Application Ser. No. 60/039,485, filed Feb. 28,1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to wheelchairs and moreparticularly to an anti-rollback assembly that operatively associateswith a wheelchair to prevent the wheelchair from rolling backwards andaway from its occupant as the occupant attempts to mount or dismount thewheelchair, yet permits the wheelchair in an unoccupied state to bemoved in a forward direction.

The anti-rollback assembly of the present invention is especiallysuitable for wheelchairs of invalids, the cognitively impaired, theelderly, and sufferers of physically and mentally disabling diseasessuch as Alzheimer's.

2. Description of the Related Art

Almost all wheelchairs possess a parking brake in one form or anotherwhich, when actuated, maintains the wheelchair in a stationary positionby preventing one or both of the large drive wheels of the wheelchairfrom rotating about a common central axis. Perhaps the most crucialperiods for the wheelchair to remain stationary are when a personattempts to sit down in and occupy the wheelchair and when the occupantattempts to stand up from and vacate the wheelchair. The natural motionof a person performing these acts imparts a force in the rearwarddirection on the wheelchair, which, without the benefit of an actuatedparking brake, causes the wheelchair to move backwards and away from theperson.

As a consequence of the mental and physical infirmities suffered by manywheelchair occupants, especially patients suffering from Alzheimer'sdisease and other mental frailties, occupants often forget to actuatemanually-operated parking brakes prior to attempting to rise from thewheelchair, or neglect to inspect the parking brake to ensure it isengaged in a locked position prior to attempting to sit down into thewheelchair. Failure to engage the manually-operated parking brake in itslocked position presents a serious hazard of injury to both the occupantand his or her caretaker, since the wheelchair is unimpeded from rollingback and away from the occupant as the occupant attempts to rise from orsit down in the wheelchair.

To address the shortcomings of manually-operated parking brakes, severaldifferent automatically-operated locking brake assemblies have beenproposed. U.S. Pat. No. 5,203,433 sets forth a discussion of someconventional automatic locking brake assemblies. Each of theconventional assemblies mentioned in U.S. Pat. No. 5,203,433 ischaracterized by the provision of a locking member that, unless manuallydisengaged, prevents or at least substantially obstructs both theforward or rearward movement of the wheelchair with which the assemblyis associated when the wheelchair is unoccupied.

However, one of the most important functions served by an automaticwheelchair brake is that it not only prevent the wheelchair from rollingbackwards and away from its occupant as the occupant mounts or dismountsthe wheelchair, but that the brake also not substantially obstruct theforward motion of the wheelchair when unoccupied so that the unoccupiedwheelchair can be easily maneuvered to a desirable location for use ortemporary storage.

A long-felt need therefore exists to provide an automatically-operatedanti-rollback assembly for a wheelchair that biases a braking mechanisminto an activated position when the wheelchair is unoccupied to preventthe wheelchair from rolling back when it is mounted or dismounted innormal operation, yet, while in the activated position, permits theforward motion of the unoccupied wheelchair.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide ananti-rollback assembly that solves the aforementioned problemsassociated with the related art as well as other problems and addressesthe long-felt need outlined above.

It is another object of the present invention to provide an automaticanti-rollback assembly which is reliable in operation, easy to use, andeconomical to manufacture.

A further object of the present invention is to provide an automaticanti-rollback assembly that can be easily and inexpensively retrofittedto existing wheelchairs.

It is another object of the present invention to provide an automaticanti-rollback assembly that, when operatively associated with awheelchair, permits the unoccupied wheelchair to freely roll in aforward direction, yet impedes only the rearward motion of thewheelchair, so that the unoccupied wheelchair can be used, for example,as a walker.

Still another object of the present invention is the provision of awheelchair having an automatic anti-rollback assembly with an ambulationmonitor which activates an alarm when the wheelchair occupant attemptsto vacate the wheelchair.

In accordance with the principles of the present invention, these andother objects are attained by the provision of an automaticanti-rollback assembly that is adapted or adaptable for use incombination with a wheelchair. The automatic anti-rollback assemblygenerally comprises a one-way brake assembly supportable on a framestructure of a wheelchair, biasing member, and a brake releasingassembly. The one-way brake assembly includes a one-way brake member (orbrake arm). When used in combination with a wheelchair, the one-waybrake assembly is movable between a non-activated position in which theone-way brake member is positioned to permit the rear drive wheelassembly to rotate in forward and rearward directions to enable thewheelchair to move freely in both the forward and rearward directions,and an non-activated position in which the one-way brake member ispositioned to prevent rotation of the rear drive wheel assembly in therearward direction so as to prevent movement of the wheelchair in therearward direction, yet continues to permit rotation of the rear drivewheel assembly in the forward direction for forward movement of thewheelchair. The biasing member serves to impart a biasing force to urgethe one-way brake assembly towards the activated position. The brakereleasing assembly is operatively associated with the one-way brakeassembly and the biasing member, and is movable in response to thewheelchair being occupied to overcome the biasing force of the biasingmember so as to move the one-way brake assembly from the activatedposition to the non-activated position, thereby enabling the wheelchairto freely move in both the forward and rearward directions unencumberedby the one-way brake member.

In accordance with the present invention, the occupant of the wheelchairis not required to set a conventional parking brake. Instead, thewheelchair is automatically immobilized against backward movement by theanti-rollback device when the occupant is attempting to rise from or sithimself in the seat member. In addition, when the occupant is fullyseated in the seat member, the anti-rollback device is disengaged, i.e.,the one-way brake assembly is moved into a non-activated position, sothat the wheelchair can be freely moved forward or backwardsunencumbered by the one-way brake member.

These and other objects, features, and advantages of the presentinvention will become apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate an embodiment of the presentinvention. In such drawings:

FIG. 1 is a perspective rear view of a wheelchair including ananti-rollback assembly in accordance with a preferred embodiment of thepresent invention, in which the range of movement of the anti-rollbackassembly between non-activated and activated positions is depicted byarrows;

FIGS. 2A and 2B are side elevational views of the wheelchair of FIG. 1in occupied and unoccupied states, respectively;

FIG. 3 is an exploded view of mounting and brake releasing assemblies ofthe anti-rollback assembly of FIG. 1;

FIG. 4 is a perspective view of a bracket and brake arm supportingmember of the mounting assembly of FIGS. 1 and 3;

FIG. 5 is a rear view of the bracket of the mounting assembly depictinga biasing member;

FIG. 6 is a side view of an ambulation monitor according to oneembodiment of the present invention; and

FIG. 7 is an exploded view of the ambulation monitor of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of a conventional wheelchair structure will bediscussed hereinbelow for the purposes of assisting in the detaileddescription of the anti-rollback assembly of the present invention andexplaining the manner in which the anti-rollback assembly is operativelysupported on a wheelchair. It is understood, however, the presentinvention is not restricted to the illustrated wheelchair or theconstruction and arrangement of the individual components of theillustrated wheelchair.

Referring now to the drawings, there is shown in FIGS. 1, 2A, and 2B awheelchair generally designated by reference numeral 10. The wheelchair10 includes a frame structure 12 comprising a pair of opposing sideframes 14 a and 14 b laterally spaced from and substantially parallelwith one another. The opposing side frames 14 a and 14 b have respectivefront upright members 16 a and 16 b and respective rear upright members18 a and 18 b. In the illustrated embodiment, the front upright member16 a and the rear upright member 18 a of the side frame 14 a includelongitudinal axes oriented substantially vertical, and areinterconnected with crossbars 19 a and 20 a. The front upright member 16b and the rear upright member 18 b of the other side frame 14 b arearranged and interconnected in a similar manner with crossbars 19 b and20 b. Handles 22 a and 22 b are fitted onto upper ends (unnumbered) ofthe rear upright members 18 a and 18 b, respectively. Arm rests 24 a and24 b are secured to upper surfaces of the crossbars 19 a and 19 b,respectively.

The wheelchair 10 further includes a flexible seat member 26 extendingbetween the opposing side frames 14 a and 14 b and arranged in asubstantially horizontal orientation so as to permit an occupant to sitthereon. A flexible back support member 28 extends between the rearupright members 18 a and 18 b and, together with the seat member 26,define a seating area (unnumbered) for supporting the wheelchairoccupant.

As shown in FIG. 1, the wheelchair 10 further includes rear drive wheelassemblies comprising two large rear drive wheels 30 a and 30 b whichare manually rotatable by the occupant to rotate about hubs 32 a and 32b, respectively. The hubs 32 a and 32 b are respectively attached to therear upright members 18 a and 18 b with axle bolts (unnumbered) and eachinclude a plurality of spokes (not shown) extending therefrom tointerconnect the hubs 32 a and 32 b to their respective drive wheels 30a and 30 b. Front wheel assemblies comprise small wheels 34 a and 34 bswivably connected to the front upright members 16 a and 16 b,respectively, to facilitate turning of the wheelchair 10.

Although not shown, it is understood that in accordance with the presentinvention, the wheelchair 10 can include additional components, such asfootrests. It is further understood that in accordance with the presentinvention the wheelchair can omit one or more of the componentsdiscussed above and illustrated in the drawings, so long as thewheelchair is characterized as being capable of operatively supportingthe anti-rollback feature of the present invention.

One embodiment of the automatic anti-rollback assembly of the presentinvention, which is generally designated by reference numeral 40, willnow be described with greater specificity hereinbelow.

Referring to FIGS. 3 and 4, the illustrated automatic anti-rollbackassembly 40 includes two mounting assemblies. For explanatory purposes,only one of the two mounting assemblies, which is generally designatedby reference numeral 42, will be described below.

The mounting assembly 42 includes a mounting bracket 44 with adiscontinuous circular clamping end 46, which accommodates the rearupright member 18 a. Nut-bolt combinations 48 and 50 serve to secure themounting bracket 44 to the rear upright member 18 a. Reinforcementspacers 52 may be used in combination with the nut-bolt combinations 48and 50 to prevent bowing of the bolts. The reinforcement spacers 52 canbe made of, for example, nylon or other plastics. As shown in FIGS. 1,2A, and 2B, the clamping end 46 of the mounting bracket 44 is positionedimmediately above the axle bolt associated with hub 32 a.

The mounting assembly 42 further includes a movable brake-arm supportingmember 54 (also referred to as a brake-member supporting member orpivotable collar), which is substantially configured as a clevis yoke.In the illustrated embodiment, the brake-arm supporting member 54 isrotatable about its longitudinal axis between first and secondpositions. Opposing sides of the mounting bracket 44 define alignedapertures, one of which is designated by reference numeral 56 in FIG. 4.The apertures 56 are sized to receive a shaft 58 co-axially extendingfrom and integral with the pivotable collar 54. The shaft 58 is securedto the mounting bracket 44 with, for example, a lock cap 60. As shown inFIG. 5, a torsion spring 62 is accommodated in the mounting bracket 44and connected to the shaft 58 of the pivotable collar 54 via pin 63 tourge the pivotable collar 54 into its first position.

The opposite end (unnumbered) of the pivotable collar 54 defines a slot66 diametrically positioned and axially extending a certain depth intopivotable collar 54. A first bore 68 is diametrically defined within thepivotable collar 54, and arranged orthogonally relative to the slot 66to intersect the slot 66. Second and third bores 70 and 72 are eachdiametrically disposed, arranged orthogonally relative to each other tointersect each other, and are interposed between the slot 66 and theshaft 58. The functions of the slot 66 and the first, second, and thirdbores 68, 70, and 72 will be described below.

Still referring to FIG. 3, the automatic anti-rollback assembly 40further includes a brake releasing assembly, which is generallydesignated by reference numeral 74.

The brake releasing assembly 74 includes a substantially L-shapedactuator lever 76, adjustor plate 78, and connector plates 80. Forexplanatory purposes, the connector plate 80 and the side of theadjustor plate 78 operatively associated with mounting assembly 42 willbe described below.

The actuator lever 76 is cantilevered at a central portion (unnumbered)of the adjustor plate 78. The end (unnumbered) of the adjustor plate 78defines an exposed lateral port 82, which receives a portion of theconnector plate 80. The upper region of the adjustor plate 78 has anelongated slot 84 defined therethrough in communication with the lateralport 82. (As shown in FIG. 3, the slots 84 are located on each side ofthe central portion of the adjustor plate 78.) A nut-washer combination86 engages a first aperture 88 of the connector plate 80 and theelongated slot 84 to thereby secure the adjustor plate 78 to theconnector plate 80. The end of the connector plate 80 opposite to thefirst aperture 88 defines a second aperture 90.

As shown in FIGS. 2A and 2B, when the brake releasing assembly 74 isconnected to the mounting assembly 42, the brake releasing assembly 74is positioned immediately underneath the seat member 26. The connectionof the brake releasing assembly 74 to the mounting assembly 42 will nowbe described with reference to FIG. 3.

The slot 66 of the pivotable collar 54 receives the end of the adjustorplate 78 containing the second aperture 90 so that the first bore 68 andthe second aperture 90 are aligned. A quick-release pin 92 is insertedthrough the aligned first bore 68 and second aperture 90 to secure thebrake releasing assembly 74 to the mounting assembly 42. The provisionof the quick-release pin 92 or similar connecting device facilitates thequick and easy separation and removal of the brake releasing assembly74. When the wheelchair 10 is of the collapsible variety, the frames 14a and 14 b and associated wheels on either side of the seat member 26can thereby be folded together for convenient stowage. The provision ofa quick-releasing mechanism to facilitate the ability of the wheelchair10 to be collapsed and stored represents one of the many advantages ofthe present invention.

Another of the advantages of the illustrated embodiment rests in theconfiguration of the elongated slots 84 of the adjustor plate 78, whichprovides for an adjustable positional relationship with the firstaperture 88 of connector plate 80. This feature makes the illustratedanti-rollback assembly 40 adaptable and retrofittable to wheelchairs ofvarious widths. Although not shown, it is noted that the elongated slots84 can be replaced with, for example, a series of spaced apertures.

The anti-rollback assembly 40 also includes a brake member (or brakearm) 94, a proximal end portion 96 of which is received in the secondbore 70 of the pivotable collar 54 and secured thereto with a set screw98 (FIG. 3). (The brake member 94 and mounting assembly 42 collectivelyform a one-way brake assembly in this embodiment.) As respectively shownin FIGS. 2A and 2B, a distal end portion 99 of the brake arm 94 eitheris spaced from a rear region of the drive wheel 30 a (when thewheelchair 10 is occupied) or rests on the drive wheel 30 a (when thewheelchair 10 is unoccupied or the occupant attempts to rise from or sitdown into the wheelchair 10). As is believed evident from thisdescription, the positional relationship of the brake arm 94 to thepivotable collar 54 can be adjusted (by loosening set screw 98) to makethe brake arm 94 adaptable and retrofittable to wheelchairs of variousdrive wheel sizes.

The operational movement of the anti-rollback assembly 40 will bedescribed below with reference to FIGS. 1, 2A, 2B, and 3.

In its unoccupied state, the torsion spring 62 imparts a biasing forceto urge the brake-arm supporting member 54 towards the first position,which in turn urges the seat member 26 towards its upper position andthe distal end portion 99 of the brake arm 94 into the activatedposition. As is seen from the arrows in FIGS. 1, 2A, and 2B, in theillustrated embodiment the axis of the pivotal collar 54 is locatedhigher and to the rear of the axis of the drive wheels 30 a and 30 b. Asa consequence, the torsion spring 62 applies a biasing force along anon-radial direction relative to the drive wheels 30 a and 30 b. Asshown by the arrows in FIGS. 1, 2A, and 2B, this biasing force urges theend portion 99 along a direction substantially parallel to a tangent atthe point at which the brake arm end portion 99 engages the peripheralsurface of the associated drive wheel. In this manner, the end portion99 pivots upward and downward on a smaller and intersecting arc to thatof the associated drive wheel. In the activated position, the distal endportion 99 of the brake arm 94 prevents the first drive wheel 30 a fromrotating about a central axis thereof in a rearward direction, yet doesnot prevent the first drive wheel 30 a from rotating about the centralaxis thereof in a forward direction.

When a patient attempts to rest into the seating area of the wheelchair10, the weight of the patient imparts a downward force on the seatmember 26, which causes the seat member 26 to flex, bend, slide, orotherwise move in a downward direction to its lower position. Thedownward movement of the seat member 26 translates the downward force tothe actuator lever 76, thereby pivoting the actuator lever 76 downwardas indicated by the arrow in FIG. 2A. As the actuator lever 76 pivots,the adjustor plate 78 is rotated about its longitudinal axis totranslate a corresponding rotational movement to pivotable collar 54. Asthe collar 54 rotates about its axis, the brake arm 94 operativelyassociated therewith is pivoted about the region of its proximal endportion 96 accommodated in the second bore 70 so that the distal endportion 99 is moved substantially along the forward rotational directionfrom the activated position to a non-activated position. In thenon-activated position, the distal end portion 99 is radially spacedfrom the drive wheel 30 a and, hence, does not interfere with manualoperation (including both forward and rearward motion) of the wheelchair10.

Conversely, when an occupant of the wheelchair 10 attempts to rise fromthe seating area, the torsion spring 62 imparts a biasing force to urgethe brake-arm supporting member 54 towards the first position, which inturn urges the seat member 26 towards its upper position and the distalend portion 99 of the brake arm 94 to move in a downward manner along anarcuate path (as shown by the arrow in FIG. 2B), that is, substantiallyalong a rearward rotational direction into the activated position.

In the illustrated embodiment, the arcuate path that the distal endportion 99 of the brake arm 94 follows between the activated andnon-activated positions intersects the circumference of the drive wheel30 a. Consequently, the amount of frictional force applied to the brakearm 94 by the drive wheel 30 a is proportional to the rearward forceapplied to the wheelchair 10. Stated differently, when the wheelchair 10is moved rearwardly, frictional force between the drive wheel 30 a andthe brake arm 94 causes the distal end portion 99 of the brake arm 94 tomove in a generally radially inward direction towards the hub 32 a,which further presses the distal end portion 99 into the drive wheel 30a. Consequently, continued rearward motion of the wheelchair 10 has acorresponding immobilizing effect on the drive wheel 30 a of thewheelchair 10.

Accordingly, even though the occupant of the wheelchair 10 may neglectto set a conventional parking brake (not shown), the chair 10 isautomatically immobilized against backward movement by the anti-rollbackdevice when the occupant is attempting to rise from or seat himself inthe seat member 26.

Referring now to FIGS. 6 and 7, according to another embodiment of thepresent invention the wheelchair is equipped with an ambulation monitor,generally designated by reference numeral 100, for activating an alarmwhen the occupant of the wheelchair 10 attempts to rise from the seatmember 26.

As shown in FIG. 7, the ambulation monitor includes a housing structure102, which houses a horn 104, an on/off switch 106 and a switch jack 108electrically connected to the horn 104, and an energy source 110, e.g.,a battery, electrically connected to the on/off switch 106. The housingstructure 102 is supported on the mounting bracket 44 with a mountingbracket 112, a mounting bracket clamp knob 114, and screws 116 a and 116b.

Referring now to FIG. 6, a connector wire 120 electrically connects theswitch jack 108 to a cam actuator switch 122. A cam 124 is cooperativelyassociated with the pivotable collar 54 by providing the cam 124 with aneccentrically disposed aperture 126 through which a portion of thepivotable collar 54 is disposed. Accordingly, when the occupant beginsto rise from the seat member 26, the pivotable collar 54 is rotatedabout its longitudinal axis as described above. The cam 124, by virtueof its cooperative association with the pivotable collar 54, rotates toactuate the switch 122, thereby activating the horn 104 to alert staffof the occurrence.

In its broadest aspects, several variations and modifications to theabove-discussed anti-rollback assembly can be implemented withoutdeparting from the scope of the present invention. For example, theanti-rollback assembly 40 may include a separate biasing member ormembers, such as springs, to urge the seat member into its upperposition independent of or in conjunction with the torsion spring 62.Also, although in the illustrated embodiment each of the drive wheels 30a and 30 b and a one-way brake assembly (that is, a mounting assemblyand brake arm) associated therewith, it is understood that theanti-rollback assembly 40 may include only one mounting assembly 42 andbrake arm 94, in which case, for example, a pivotable bar (not shown)may interconnect the brake releasing assembly 74 with the side frame 14b not associated with the mounting assembly 42 and brake arm 94. Wherethe anti-rollback assembly includes one-way brake assembliesrespectively associated with each of the drive wheels 30 a and 30 b (asshown in FIGS. 1, 2A, and 2B), a second torsion spring (not shown) maybe accommodated in the mounting bracket associated with the second drivewheel 30 b; alternatively, the anti-rollback assembly 40 may includeonly a single torsion spring, since the pivotable collar 54 associatedwith the first drive wheel 30 a rotates in unison with the pivotablecollar associated with the second drive wheel 30 b due to theinterconnection provided by the brake releasing assembly 74.

The one-way brake assemblies may respectively engage portions of therear drive wheel assemblies at positions other than the rear drivewheel. For example, although not shown, the assemblies could includeratchet and pawl wheel assemblies to accomplish the anti-rollbackfunction of the present invention.

These and other modifications to the assembly, when viewed withreference to this disclosure, are within the purview of those skilled inthe art.

If desired, the automatic anti-rollback assembly 40 of the presentinvention may be used in conjunction with conventional supplementalbraking devices well known in the art, including, for example, amanually-operated parking brake to immobilize the wheelchair fromforward or rearward movement when occupied.

The foregoing detailed description of the preferred embodiments of theinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise embodiments disclosed. The embodiments werechosen and described in order to best explain the principles of theinvention and its practical application, thereby enabling others skilledin the art to understand the invention. While the invention has beendescribed in connection with what is presently considered to be the mostpractical and preferred embodiments, it is understood that the inventionis not limited to the disclosed embodiments, but, on the contrary, isintended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of the appended claims.

What is claimed is:
 1. A wheelchair comprising: a frame structure; arear drive wheel assembly and a front wheel assembly supporting saidframe structure, said rear drive wheel assembly comprising first andsecond drive wheels that have respective rotational axes and are eachrotatable relative to said frame structure along a forward rotationaldirection which causes said wheelchair to move forward and a rearwardrotational direction which causes said wheelchair to move rearward; aseat member supported by said frame structure and constructed andoriented to accommodate an occupant; a one-way brake assembly comprisinga brake member having at least one end portion movable from an activatedstate in which said end portion engages at least one of said drivewheels at a point of contact to a non-activated state in which said endportion is spaced from the point of contact of said at least one of saiddrive wheels so as not to interfere with rotation of said at least oneof said drive wheels in the forward and rearward rotational directions;a biasing member operatively associated with said one-way brake assemblyto exert a biasing force on said brake member, the biasing force urgingsaid end portion into engagement with the point of contact withsufficient force to maintain engagement between said end portion and thepoint of contact and prevent rearward rotation of said at least one ofsaid drive wheels when said end portion is in the activated state, yetthe biasing force exerted by said biasing member on said brake memberbeing insufficient to cause said end portion to prevent forward rotationof said at least one of said drive wheels when in the activated state;and an automatic brake releasing assembly operatively associated withsaid one-way brake assembly and said seat member to automatically movesaid end portion away from the point of contact and out of the activatedstate to the non-activated state in response to occupation of said seatmember.
 2. The wheelchair according to claim 1, wherein the point ofcontact is at an outer peripheral surface of said at least one of saiddrive wheels.
 3. The wheelchair according to claim 1, wherein saidbiasing member urges said seat member upward.
 4. The wheelchairaccording to claim 1, wherein said end portion follows an arcuate pathbetween the activated and the non-activated states.
 5. The wheelchairaccording to claim 4, wherein said end portion moves substantially alongthe forward rotational direction from the activated state in which saidend portion engages at least one of said drive wheels at the point ofcontact to the non-activated state.
 6. The wheelchair according to claim1, wherein said biasing member comprises a torsion spring.
 7. Thewheelchair according to claim 1, further comprising an ambulationmonitor operative to activate an alarm when the occupant rises from saidseat member.
 8. The wheelchair according to claim 1, wherein the pointof contact is rearward of said rotational axes.
 9. A wheelchaircomprising: a frame structure; a rear drive wheel assembly and a frontwheel assembly supporting said frame structure, said rear drive wheelassembly comprising first and second drive wheels that have respectiverotational axes and are each rotatable relative to said frame structurealong a forward rotational direction which causes said wheelchair tomove forward and a rearward rotational direction which causes saidwheelchair to move rearward; a seat member supported by said framestructure and constructed and oriented to accommodate an occupant; atleast one first one-way brake assembly comprising a first brake memberhaving a first end portion movable from an activated state in which saidfirst end portion engages said first drive wheel at a point of contacton said first drive wheel to a non-activated state in which said endportion is spaced from the point of contact of said first drive wheel soas not to interfere with rotation of said first drive wheel in theforward and rearward rotational directions; a second one-way brakeassembly comprising a second brake member having a second end portionmovable from the activated state in which said second end portionengages said second drive wheel at a point of contact on said seconddrive wheel to the non-activated state in which said end portion isspaced from the point of contact of said second drive wheel so as not tointerfere with rotation of said second drive wheel in the forward andrearward rotational directions; at least one biasing member operativelyassociated with said one-way brake assemblies to exert a biasing forceon said brake members, the biasing force urging said first and secondend portions into respective engagement with said first and second drivewheels at the points of contact with sufficient force to maintainengagement between said end portions and the respective points ofcontact and prevent rearward rotation of said first and second drivewheels when said first and second end portions are in the activatedstate, yet the biasing force exerted by said biasing member on saidbrake members being insufficient to cause said first and second endportions to prevent forward rotation of said first and second drivewheels when in the activated state; and at least one automatic brakereleasing assembly operatively associated with said first and secondone-way brake assemblies and said seat member to automatically move saidend portions away from the points of contact and out of the activatedstate to the non-activated state in response to occupation of said seatmember.
 10. The wheelchair according to claim 9, wherein the points ofcontact are outer peripheral surfaces of said first and second drivewheels, respectively.
 11. The wheelchair according to claim 9, whereinsaid biasing member urges said seat member upward.
 12. The wheelchairaccording to claim 9, wherein said end portions follow arcuate pathsbetween the activated and the non-activated states.
 13. The wheelchairaccording to claim 12, wherein said first and second end portions movesubstantially along the forward rotational direction from the activatedstate in which said first and second end portions respectively engagesaid first and second drive wheels at the points of contact to thenon-activated state.
 14. The wheelchair according to claim 9, whereinsaid biasing member comprises a torsion spring.
 15. The wheelchairaccording to claim 9, further comprising an ambulation monitor operableto activate an alarm when the occupant rises from said seat member. 16.The wheelchair according to claim 9, wherein the points of contact arerearward of said rotational axes.
 17. The wheelchair according to claim9, wherein said at least one biasing member comprises first and secondbiasing members applying the biasing force to said first and second endportions, respectively.
 18. The wheelchair according to claim 9, whereinsaid first one-way brake assembly and said second one-way brake assemblyare operatively connected to move in tandem between the activated andthe non-activated states.
 19. An anti-rollback assembly for a wheelchaircomprising a frame structure, a seat member constructed and oriented toaccommodate an occupant, and a rear drive wheel assembly and a frontwheel assembly carrying the frame structure and comprising first andsecond drive wheels and first and second front wheels, respectively,said anti-rollback assembly comprising: first and second mountingbrackets mountable on the frame structure; first and second pivotalcollars pivotally supported by said mounting brackets; an automaticbrake releasing subassembly; a connecting subassembly operativelyconnecting said first and second collars to each other and to saidautomatic brake releasing subassembly so that movement of said automaticbrake releasing subassembly relative to said mounting brackets pivotssaid first and second pivotal collars in unison; a first brake armhaving a first distal end portion and a second brake arm having a seconddistal end portion, said first and second brake arms being connected tosaid first and second pivotal collars, respectively, so that pivotalmovement of said first and second pivotal collars relative to saidmounting brackets guides said first and second distal end portions alongrespective arcuate paths; and at least one biasing member exerting abiasing force on said first and second pivotal collars, wherein saidfirst and second mounting brackets are mountable on the frame structureto position said automatic brake releasing subassembly under the seatmember and said first and second distal end portions in contact with thefirst and second drive wheels, respectively, causing said biasing memberto urge said first and second distal portions into contact with thefirst and second drive wheels with sufficient force to prevent rearwardrotation of the drive wheels, yet permitting said automatic brakereleasing assembly to automatically move said distal end portions alongarcuate paths out of contact with the drive wheels in response tooccupation of the seat member.
 20. The anti-rollback assembly of claim19, wherein the biasing force exerted by said biasing member on saidfirst and second brake arms is insufficient to cause said first andsecond end portions to prevent forward rotation of the first and seconddrive wheels.
 21. The anti-rollback assembly of claim 19, wherein saidconnecting subassembly being adjustable in length to permit adjustmentto a distance between the first and second collars.
 22. Theanti-rollback assembly of claim 19, wherein said first and secondpivotal collars having apertures in which said first and second brakearms are received and slidable to adjust a distance between the firstand second distal end portions and the first and second pivotal collars.